1. Field of the Invention
The present invention relates to a stream encryption device, method and program which realize an encryption process in words unit by using a clock controller.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In recent years, various kinds of services utilizing computers have been provided. In many such services, ciphers are used to realize securing of communication. The most common encryption method is a common key cryptosystem in which one key performs encryption and decryption. This common key cryptosystem is roughly classified into two methods, namely a block encryption method and a stream encryption method. The former method is the method used most commonly. The latter method is superior in processing speed than the former method, thereby attracting attention.
An example of a method and a device for generating the above-described stream cipher is disclosed in the following patent document.    Patent Document 1: Published Japanese Translation No. 2002-536912 of the PCT International Publication.
In a stream encryption method, an encryption process is performed in units of bits, wherein clock control is used as one of the most common components. However, in a stream encryption method, an encryption process is performed in units of words, wherein a keystream of word length×N (N denotes number of clocks) is canceled by the clock control, thereby impairing the efficiency of the encryption and decryption considerably. Therefore, the clock control is not used.
Moreover, since the stream encryption methods do not have an independent key schedule algorithm, the security problem has been pointed out such that leakage of an internal state thereof can cause partial leakage of a secret key. Further, there has been a difficulty in establishing countermeasures regarding recovery when deviation in the synchronization occurs between sender and receiver (encryption/decryption).
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure. The present invention has been achieved on the basis of the above circumstances.